Manchester United's Wayne Rooney injured

Wayne Rooney had been having an uneven season when he injured his knee.

Matthew Peters/Man Utd via/Getty Images

MANCHESTER, England (AP) -- Manchester United striker Wayne Rooney will miss up to three weeks with a knee injury.

Manager Alex Ferguson says he strained a ligament behind the knee when he tried to hit a volley late in practice Tuesday.

The England star missed United's 4-3 win over Newcastle on Wednesday. Ferguson didn't specify which knee was injured.